1. Field of the Invention
The present invention relates generally to a control method for an external control type fan clutch of the type, in which the fan rotations for cooling an internal combustion engine of an automobile or the like are controlled according to a change in the ambient temperature or the rotation.
2. Description of the Related Art
In the prior art, there is an external control type fan clutch of this kind (as referred to JP-C-2911623, JP-A-2003-239741 and JP-A-9-119455). A sealed casing, which is composed of a nonmagnetic case borne through a bearing on a rotary shaft having a drive disc fixed at its leading end and a cover attached to the case, has its inside partitioned by a partition into an oil reservoir chamber and a torque transmission chamber having the drive disc fitted therein. The fan clutch is provided with a dam in a portion of the inner circumference wall of the cover opposed to the outer circumference wall of the drive disc, in which the oil collects at a rotating time, and a magnetic valve member leading to the dam and disposed in the oil reservoir chamber for opening/closing an oil circulation passage formed between the torque transmission chamber and the oil reservoir chamber. On the oil reservoir chamber side of the sealed casing, an electromagnet is supported on the rotary shaft through a bearing, and the valve member is activated by the electromagnet to control the On/Off of the oil circulation passage so that the effective contact area of the oil is increased/decreased in the torque transmission clearance formed between the drive side and the driven side thereby to control the rotating torque transmission from the drive side to the driven side. In the external control type fan clutch thus configured, the On/Off of the valve member is controlled by a PID control (i.e., a feedback control method by proportion, differentiation and integration) on the basis of at least one signal of a radiator cooling liquid temperature, a fan speed, a transmission oil temperature, a vehicle speed, an engine speed, the compressor pressure of an air conditioner, and an On/Off signal of the air conditioner. In another similar external control type fan clutch controlling method, a valve member is activated by an electromagnet to control the On/Off of an oil circulation passage and in which the effective contact area of oil in a torque transmission clearance between the drive side and the driven side is increased/decreased to control the rotating torque transmission from the drive side to the driven side. In this external control type fan clutch, moreover, a ring-shaped magnetic element is arranged between the electromagnet and the valve member and is so assembled in the sealed casing that its magnetic flux may be transmitted to the valve member through the magnetic element. In this fan clutch, the fan clutch is controlled by a PID control (i.e., a feedback control method by proportion, differentiation and integration) by setting the upper limit speed for an optimum fan speed demanded by the engine side, by temporarily stopping a fan speed control signal on the basis of a speed difference among the engine speed, the fan speed and the optimum fan speed, by temporarily stopping (or cutting) the fan speed control signal on the basis of the engine acceleration or the accelerator (throttle) position acceleration, or by restricting the change in the optimum fan speed on the basis of the changing rate of the optimum fan speed (as referred to Japanese Patent Application 2004-113606).
According to the method for controlling the external control type fan clutch, as disclosed in Japanese Patent Application 2004-113606, the fan rotation can be controlled to be always confined within the satisfactory temperature range of the engine combustion efficiency by controlling the temperature of the radiator cooling liquid as a direct control parameter. The fan rotation for the satisfactory condenser cooling efficiency of the air conditioner can be kept to improve the air conditioner cooling performance by detecting the On/Off situation of the air conditioner and the compressor pressure at all times. By detecting the engine speed and the accelerator opening, moreover, the fan can be prevented from being dragged by the starting acceleration or the passing acceleration from the idling time and the noise of fan can be reduced. By making use of means for setting the upper limit speed for the optimum fan speed demanded by the engine side, for temporarily stopping (or cutting) the fan speed control signal on the basis of the speed difference among the engine speed, the fan speed and the optimum fan speed, for temporarily stopping (or cutting) the fan speed control signal on the basis of the engine acceleration or the accelerator (throttle) position acceleration, or for restricting the change in the optimum fan speed on the basis of the changing rate of the optimum fan speed, moreover, there are obtained many excellent effects not only to reduce the delay in the response to the control instruction of the fan rotation, to reduce the dragging at the time of varying the engine speed or starting the engine, and to stabilize the fan rotation behaviors but also to reduce the horsepower to be consumed by the fan (or to improve the mileage) and to reduce the fan noises.
In case the individual PID gains (or proportional gains) are constant, however, the external control type fan clutch controlling method, as disclosed in Patent Publication 4 adopting the PID control in the fan rotation control method, cannot not properly respond to variations in the demanded fan speed, the engine speed or the state of the fan clutch. Thus, the fan clutch is defective in the degraded mileage, the drop in the cooling efficiency of the air conditioner (A/C), or in that it cannot suppress the generation of fan noises due to the unnecessary dragging of the fan rotation at the acceleration time, so that it cannot optimize the fan rotation control.